We propose to determine the sequence of bovine heart cytochrome oxidase and the Pseudomonas putida cytochrome P-450. Cytochrome oxidase has seven different subunits and we also hope to determine the correct prosthetic group (heme a and copper)-subunit assignment. The prosthetic group binding regions and the heme ligands will be investigated. In the case of the cytochrome P-450, we hope to determine the heme binding site and the heme ligands as well as the location of the two cysteine residues which are required for the electron transfer reactions. It should be mentioned that this is a renewal grant request and that the sequence investigations are already in progress.